[ViewVC] Diff of: cvs/Coro/Coro.pm

Comparing Coro/Coro.pm (file contents):
Revision 1.114 by root, Wed Jan 24 16:22:08 2007 UTC vs.
Revision 1.270 by root, Thu Oct 1 23:50:23 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	Coro - coroutine process abstraction	3	Coro - the only real threads in perl
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use Coro;	7	use Coro;
8		8
9	async {	9	async {
10	# some asynchronous thread of execution	10	# some asynchronous thread of execution
		11	print "2\n";
		12	cede; # yield back to main
		13	print "4\n";
11	};	14	};
12		15	print "1\n";
13	# alternatively create an async coroutine like this:	16	cede; # yield to coro
14		17	print "3\n";
15	sub some_func : Coro {	18	cede; # and again
16	# some more async code	19
17	}	20	# use locking
18		21	use Coro::Semaphore;
19	cede;	22	my $lock = new Coro::Semaphore;
		23	my $locked;
		24
		25	$lock->down;
		26	$locked = 1;
		27	$lock->up;
20		28
21	=head1 DESCRIPTION	29	=head1 DESCRIPTION
22		30
23	This module collection manages coroutines. Coroutines are similar	31	For a tutorial-style introduction, please read the L<Coro::Intro>
24	to threads but don't run in parallel at the same time even on SMP	32	manpage. This manpage mainly contains reference information.
25	machines. The specific flavor of coroutine use din this module also
26	guarentees you that it will not switch between coroutines unless
27	necessary, at easily-identified points in your program, so locking and
28	parallel access are rarely an issue, making coroutine programming much
29	safer than threads programming.
30		33
31	(Perl, however, does not natively support real threads but instead does a	34	This module collection manages continuations in general, most often in
32	very slow and memory-intensive emulation of processes using threads. This	35	the form of cooperative threads (also called coros, or simply "coro"
33	is a performance win on Windows machines, and a loss everywhere else).	36	in the documentation). They are similar to kernel threads but don't (in
		37	general) run in parallel at the same time even on SMP machines. The
		38	specific flavor of thread offered by this module also guarantees you that
		39	it will not switch between threads unless necessary, at easily-identified
		40	points in your program, so locking and parallel access are rarely an
		41	issue, making thread programming much safer and easier than using other
		42	thread models.
34		43
		44	Unlike the so-called "Perl threads" (which are not actually real threads
		45	but only the windows process emulation (see section of same name for more
		46	details) ported to unix, and as such act as processes), Coro provides
		47	a full shared address space, which makes communication between threads
		48	very easy. And Coro's threads are fast, too: disabling the Windows
		49	process emulation code in your perl and using Coro can easily result in
		50	a two to four times speed increase for your programs. A parallel matrix
		51	multiplication benchmark runs over 300 times faster on a single core than
		52	perl's pseudo-threads on a quad core using all four cores.
		53
		54	Coro achieves that by supporting multiple running interpreters that share
		55	data, which is especially useful to code pseudo-parallel processes and
		56	for event-based programming, such as multiple HTTP-GET requests running
		57	concurrently. See L<Coro::AnyEvent> to learn more on how to integrate Coro
		58	into an event-based environment.
		59
35	In this module, coroutines are defined as "callchain + lexical variables +	60	In this module, a thread is defined as "callchain + lexical variables +
36	@_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain,	61	some package variables + C stack), that is, a thread has its own callchain,
37	its own set of lexicals and its own set of perls most important global	62	its own set of lexicals and its own set of perls most important global
38	variables.	63	variables (see L<Coro::State> for more configuration and background info).
		64
		65	See also the C<SEE ALSO> section at the end of this document - the Coro
		66	module family is quite large.
39		67
40	=cut	68	=cut
41		69
42	package Coro;	70	package Coro;
43		71
44	use strict;	72	use common::sense;
45	no warnings "uninitialized";	73
		74	use Carp ();
		75
		76	use Guard ();
46		77
47	use Coro::State;	78	use Coro::State;
48		79
49	use base qw(Coro::State Exporter);	80	use base qw(Coro::State Exporter);
50		81
51	our $idle; # idle handler	82	our $idle; # idle handler
52	our $main; # main coroutine	83	our $main; # main coro
53	our $current; # current coroutine	84	our $current; # current coro
54		85
55	our $VERSION = '3.5';	86	our $VERSION = 5.17;
56		87
57	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);	88	our @EXPORT = qw(async async_pool cede schedule terminate current unblock_sub);
58	our %EXPORT_TAGS = (	89	our %EXPORT_TAGS = (
59	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],	90	prio => [qw(PRIO_MAX PRIO_HIGH PRIO_NORMAL PRIO_LOW PRIO_IDLE PRIO_MIN)],
60	);	91	);
61	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));	92	our @EXPORT_OK = (@{$EXPORT_TAGS{prio}}, qw(nready));
62		93
63	{	94	=head1 GLOBAL VARIABLES
64	my @async;
65	my $init;
66
67	# this way of handling attributes simply is NOT scalable ;()
68	sub import {
69	no strict 'refs';
70
71	Coro->export_to_level (1, @_);
72
73	my $old = *{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"}{CODE};
74	*{(caller)[0]."::MODIFY_CODE_ATTRIBUTES"} = sub {
75	my ($package, $ref) = (shift, shift);
76	my @attrs;
77	for (@_) {
78	if ($_ eq "Coro") {
79	push @async, $ref;
80	unless ($init++) {
81	eval q{
82	sub INIT {
83	&async(pop @async) while @async;
84	}
85	};
86	}
87	} else {
88	push @attrs, $_;
89	}
90	}
91	return $old ? $old->($package, $ref, @attrs) : @attrs;
92	};
93	}
94
95	}
96		95
97	=over 4	96	=over 4
98		97
99	=item $main	98	=item $Coro::main
100		99
101	This coroutine represents the main program.	100	This variable stores the Coro object that represents the main
		101	program. While you cna C<ready> it and do most other things you can do to
		102	coro, it is mainly useful to compare again C<$Coro::current>, to see
		103	whether you are running in the main program or not.
102		104
103	=cut	105	=cut
104		106
105	$main = new Coro;	107	# $main is now being initialised by Coro::State
106		108
107	=item $current (or as function: current)	109	=item $Coro::current
108		110
109	The current coroutine (the last coroutine switched to). The initial value	111	The Coro object representing the current coro (the last
		112	coro that the Coro scheduler switched to). The initial value is
110	is C<$main> (of course).	113	C<$Coro::main> (of course).
111		114
112	This variable is B<strictly> I<read-only>. It is provided for performance	115	This variable is B<strictly> I<read-only>. You can take copies of the
113	reasons. If performance is not essentiel you are encouraged to use the	116	value stored in it and use it as any other Coro object, but you must
114	C<Coro::current> function instead.	117	not otherwise modify the variable itself.
115		118
116	=cut	119	=cut
117		120
118	# maybe some other module used Coro::Specific before...
119	$main->{specific} = $current->{specific}
120	if $current;
121
122	_set_current $main;
123
124	sub current() { $current }	121	sub current() { $current } # [DEPRECATED]
125		122
126	=item $idle	123	=item $Coro::idle
127		124
128	A callback that is called whenever the scheduler finds no ready coroutines	125	This variable is mainly useful to integrate Coro into event loops. It is
		126	usually better to rely on L<Coro::AnyEvent> or L<Coro::EV>, as this is
		127	pretty low-level functionality.
		128
		129	This variable stores a Coro object that is put into the ready queue when
		130	there are no other ready threads (without invoking any ready hooks).
		131
129	to run. The default implementation prints "FATAL: deadlock detected" and	132	The default implementation dies with "FATAL: deadlock detected.", followed
130	exits, because the program has no other way to continue.	133	by a thread listing, because the program has no other way to continue.
131		134
132	This hook is overwritten by modules such as C<Coro::Timer> and	135	This hook is overwritten by modules such as C<Coro::EV> and
133	C<Coro::Event> to wait on an external event that hopefully wake up a	136	C<Coro::AnyEvent> to wait on an external event that hopefully wake up a
134	coroutine so the scheduler can run it.	137	coro so the scheduler can run it.
135		138
136	Please note that if your callback recursively invokes perl (e.g. for event	139	See L<Coro::EV> or L<Coro::AnyEvent> for examples of using this technique.
137	handlers), then it must be prepared to be called recursively.
138		140
139	=cut	141	=cut
140		142
141	$idle = sub {	143	$idle = new Coro sub {
142	require Carp;	144	require Coro::Debug;
143	Carp::croak ("FATAL: deadlock detected");	145	die "FATAL: deadlock detected.\n"
		146	. Coro::Debug::ps_listing ();
144	};	147	};
145		148
146	sub _cancel {
147	my ($self) = @_;
148
149	# free coroutine data and mark as destructed
150	$self->_destroy
151	or return;
152
153	# call all destruction callbacks
154	$_->(@{$self->{status}})
155	for @{(delete $self->{destroy_cb}) \|\| []};
156	}
157
158	# this coroutine is necessary because a coroutine	149	# this coro is necessary because a coro
159	# cannot destroy itself.	150	# cannot destroy itself.
160	my @destroy;	151	our @destroy;
161	my $manager;	152	our $manager;
162		153
163	$manager = new Coro sub {	154	$manager = new Coro sub {
164	while () {	155	while () {
165	(shift @destroy)->_cancel	156	Coro::State::cancel shift @destroy
166	while @destroy;	157	while @destroy;
167		158
168	&schedule;	159	&schedule;
169	}	160	}
170	};	161	};
171		162	$manager->{desc} = "[coro manager]";
172	$manager->prio (PRIO_MAX);	163	$manager->prio (PRIO_MAX);
173		164
174	# static methods. not really.
175
176	=back	165	=back
177		166
178	=head2 STATIC METHODS	167	=head1 SIMPLE CORO CREATION
179
180	Static methods are actually functions that operate on the current coroutine only.
181		168
182	=over 4	169	=over 4
183		170
184	=item async { ... } [@args...]	171	=item async { ... } [@args...]
185		172
186	Create a new asynchronous coroutine and return it's coroutine object	173	Create a new coro and return its Coro object (usually
187	(usually unused). When the sub returns the new coroutine is automatically	174	unused). The coro will be put into the ready queue, so
		175	it will start running automatically on the next scheduler run.
		176
		177	The first argument is a codeblock/closure that should be executed in the
		178	coro. When it returns argument returns the coro is automatically
188	terminated.	179	terminated.
189		180
190	Calling C<exit> in a coroutine will not work correctly, so do not do that.	181	The remaining arguments are passed as arguments to the closure.
191		182
192	When the coroutine dies, the program will exit, just as in the main	183	See the C<Coro::State::new> constructor for info about the coro
193	program.	184	environment in which coro are executed.
194		185
		186	Calling C<exit> in a coro will do the same as calling exit outside
		187	the coro. Likewise, when the coro dies, the program will exit,
		188	just as it would in the main program.
		189
		190	If you do not want that, you can provide a default C<die> handler, or
		191	simply avoid dieing (by use of C<eval>).
		192
195	# create a new coroutine that just prints its arguments	193	Example: Create a new coro that just prints its arguments.
		194
196	async {	195	async {
197	print "@_\n";	196	print "@_\n";
198	} 1,2,3,4;	197	} 1,2,3,4;
199		198
200	=cut
201
202	sub async(&@) {
203	my $coro = new Coro @_;
204	$coro->ready;
205	$coro
206	}
207
208	=item async_pool { ... } [@args...]	199	=item async_pool { ... } [@args...]
209		200
210	Similar to C<async>, but uses a coroutine pool, so you should not call	201	Similar to C<async>, but uses a coro pool, so you should not call
211	terminate or join (although you are allowed to), and you get a coroutine	202	terminate or join on it (although you are allowed to), and you get a
212	that might have executed other code already (which can be good or bad :).	203	coro that might have executed other code already (which can be good
		204	or bad :).
213		205
		206	On the plus side, this function is about twice as fast as creating (and
		207	destroying) a completely new coro, so if you need a lot of generic
		208	coros in quick successsion, use C<async_pool>, not C<async>.
		209
214	Also, the block is executed in an C<eval> context and a warning will be	210	The code block is executed in an C<eval> context and a warning will be
215	issued in case of an exception instead of terminating the program, as	211	issued in case of an exception instead of terminating the program, as
216	C<async> does. As the coroutine is being reused, stuff like C<on_destroy>	212	C<async> does. As the coro is being reused, stuff like C<on_destroy>
217	will not work in the expected way, unless you call terminate or cancel,	213	will not work in the expected way, unless you call terminate or cancel,
218	which somehow defeats the purpose of pooling.	214	which somehow defeats the purpose of pooling (but is fine in the
		215	exceptional case).
219		216
220	The priority will be reset to C<0> after each job, otherwise the coroutine	217	The priority will be reset to C<0> after each run, tracing will be
221	will be re-used "as-is".	218	disabled, the description will be reset and the default output filehandle
		219	gets restored, so you can change all these. Otherwise the coro will
		220	be re-used "as-is": most notably if you change other per-coro global
		221	stuff such as C<$/> you I<must needs> revert that change, which is most
		222	simply done by using local as in: C<< local $/ >>.
222		223
223	The pool size is limited to 8 idle coroutines (this can be adjusted by	224	The idle pool size is limited to C<8> idle coros (this can be
224	changing $Coro::POOL_SIZE), and there can be as many non-idle coros as	225	adjusted by changing $Coro::POOL_SIZE), but there can be as many non-idle
225	required.	226	coros as required.
226		227
227	If you are concerned about pooled coroutines growing a lot because a	228	If you are concerned about pooled coros growing a lot because a
228	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool {	229	single C<async_pool> used a lot of stackspace you can e.g. C<async_pool
229	terminate }> once per second or so to slowly replenish the pool.	230	{ terminate }> once per second or so to slowly replenish the pool. In
		231	addition to that, when the stacks used by a handler grows larger than 32kb
		232	(adjustable via $Coro::POOL_RSS) it will also be destroyed.
230		233
231	=cut	234	=cut
232		235
233	our $POOL_SIZE = 8;	236	our $POOL_SIZE = 8;
		237	our $POOL_RSS = 32 * 1024;
234	our @pool;	238	our @async_pool;
235		239
236	sub pool_handler {	240	sub pool_handler {
237	while () {	241	while () {
238	eval {	242	eval {
239	my ($cb, @arg) = @{ delete $current->{_invoke} or return };	243	&{&_pool_handler} while 1;
240	$cb->(@arg);
241	};	244	};
		245
242	warn $@ if $@;	246	warn $@ if $@;
243
244	last if @pool >= $POOL_SIZE;
245	push @pool, $current;
246
247	$current->prio (0);
248	schedule;
249	}	247	}
250	}	248	}
251		249
252	sub async_pool(&@) {	250	=back
253	# this is also inlined into the unlock_scheduler
254	my $coro = (pop @pool or new Coro \&pool_handler);
255		251
256	$coro->{_invoke} = [@_];	252	=head1 STATIC METHODS
257	$coro->ready;
258		253
259	$coro	254	Static methods are actually functions that implicitly operate on the
		255	current coro.
		256
		257	=over 4
		258
		259	=item schedule
		260
		261	Calls the scheduler. The scheduler will find the next coro that is
		262	to be run from the ready queue and switches to it. The next coro
		263	to be run is simply the one with the highest priority that is longest
		264	in its ready queue. If there is no coro ready, it will call the
		265	C<$Coro::idle> hook.
		266
		267	Please note that the current coro will I<not> be put into the ready
		268	queue, so calling this function usually means you will never be called
		269	again unless something else (e.g. an event handler) calls C<< ->ready >>,
		270	thus waking you up.
		271
		272	This makes C<schedule> I<the> generic method to use to block the current
		273	coro and wait for events: first you remember the current coro in
		274	a variable, then arrange for some callback of yours to call C<< ->ready
		275	>> on that once some event happens, and last you call C<schedule> to put
		276	yourself to sleep. Note that a lot of things can wake your coro up,
		277	so you need to check whether the event indeed happened, e.g. by storing the
		278	status in a variable.
		279
		280	See B<HOW TO WAIT FOR A CALLBACK>, below, for some ways to wait for callbacks.
		281
		282	=item cede
		283
		284	"Cede" to other coros. This function puts the current coro into
		285	the ready queue and calls C<schedule>, which has the effect of giving
		286	up the current "timeslice" to other coros of the same or higher
		287	priority. Once your coro gets its turn again it will automatically be
		288	resumed.
		289
		290	This function is often called C<yield> in other languages.
		291
		292	=item Coro::cede_notself
		293
		294	Works like cede, but is not exported by default and will cede to I<any>
		295	coro, regardless of priority. This is useful sometimes to ensure
		296	progress is made.
		297
		298	=item terminate [arg...]
		299
		300	Terminates the current coro with the given status values (see L<cancel>).
		301
		302	=item Coro::on_enter BLOCK, Coro::on_leave BLOCK
		303
		304	These function install enter and leave winders in the current scope. The
		305	enter block will be executed when on_enter is called and whenever the
		306	current coro is re-entered by the scheduler, while the leave block is
		307	executed whenever the current coro is blocked by the scheduler, and
		308	also when the containing scope is exited (by whatever means, be it exit,
		309	die, last etc.).
		310
		311	I<Neither invoking the scheduler, nor exceptions, are allowed within those
		312	BLOCKs>. That means: do not even think about calling C<die> without an
		313	eval, and do not even think of entering the scheduler in any way.
		314
		315	Since both BLOCKs are tied to the current scope, they will automatically
		316	be removed when the current scope exits.
		317
		318	These functions implement the same concept as C<dynamic-wind> in scheme
		319	does, and are useful when you want to localise some resource to a specific
		320	coro.
		321
		322	They slow down thread switching considerably for coros that use them
		323	(about 40% for a BLOCK with a single assignment, so thread switching is
		324	still reasonably fast if the handlers are fast).
		325
		326	These functions are best understood by an example: The following function
		327	will change the current timezone to "Antarctica/South_Pole", which
		328	requires a call to C<tzset>, but by using C<on_enter> and C<on_leave>,
		329	which remember/change the current timezone and restore the previous
		330	value, respectively, the timezone is only changed for the coro that
		331	installed those handlers.
		332
		333	use POSIX qw(tzset);
		334
		335	async {
		336	my $old_tz; # store outside TZ value here
		337
		338	Coro::on_enter {
		339	$old_tz = $ENV{TZ}; # remember the old value
		340
		341	$ENV{TZ} = "Antarctica/South_Pole";
		342	tzset; # enable new value
		343	};
		344
		345	Coro::on_leave {
		346	$ENV{TZ} = $old_tz;
		347	tzset; # restore old value
		348	};
		349
		350	# at this place, the timezone is Antarctica/South_Pole,
		351	# without disturbing the TZ of any other coro.
		352	};
		353
		354	This can be used to localise about any resource (locale, uid, current
		355	working directory etc.) to a block, despite the existance of other
		356	coros.
		357
		358	Another interesting example implements time-sliced multitasking using
		359	interval timers (this could obviously be optimised, but does the job):
		360
		361	# "timeslice" the given block
		362	sub timeslice(&) {
		363	use Time::HiRes ();
		364
		365	Coro::on_enter {
		366	# on entering the thread, we set an VTALRM handler to cede
		367	$SIG{VTALRM} = sub { cede };
		368	# and then start the interval timer
		369	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0.01, 0.01;
		370	};
		371	Coro::on_leave {
		372	# on leaving the thread, we stop the interval timer again
		373	Time::HiRes::setitimer &Time::HiRes::ITIMER_VIRTUAL, 0, 0;
		374	};
		375
		376	&{+shift};
		377	}
		378
		379	# use like this:
		380	timeslice {
		381	# The following is an endless loop that would normally
		382	# monopolise the process. Since it runs in a timesliced
		383	# environment, it will regularly cede to other threads.
		384	while () { }
		385	};
		386
		387
		388	=item killall
		389
		390	Kills/terminates/cancels all coros except the currently running one.
		391
		392	Note that while this will try to free some of the main interpreter
		393	resources if the calling coro isn't the main coro, but one
		394	cannot free all of them, so if a coro that is not the main coro
		395	calls this function, there will be some one-time resource leak.
		396
		397	=cut
		398
		399	sub killall {
		400	for (Coro::State::list) {
		401	$_->cancel
		402	if $_ != $current && UNIVERSAL::isa $_, "Coro";
		403	}
260	}	404	}
261		405
262	=item schedule	406	=back
263		407
264	Calls the scheduler. Please note that the current coroutine will not be put	408	=head1 CORO OBJECT METHODS
265	into the ready queue, so calling this function usually means you will
266	never be called again unless something else (e.g. an event handler) calls
267	ready.
268		409
269	The canonical way to wait on external events is this:	410	These are the methods you can call on coro objects (or to create
		411	them).
270		412
		413	=over 4
		414
		415	=item new Coro \&sub [, @args...]
		416
		417	Create a new coro and return it. When the sub returns, the coro
		418	automatically terminates as if C<terminate> with the returned values were
		419	called. To make the coro run you must first put it into the ready
		420	queue by calling the ready method.
		421
		422	See C<async> and C<Coro::State::new> for additional info about the
		423	coro environment.
		424
		425	=cut
		426
		427	sub _coro_run {
		428	terminate &{+shift};
		429	}
		430
		431	=item $success = $coro->ready
		432
		433	Put the given coro into the end of its ready queue (there is one
		434	queue for each priority) and return true. If the coro is already in
		435	the ready queue, do nothing and return false.
		436
		437	This ensures that the scheduler will resume this coro automatically
		438	once all the coro of higher priority and all coro of the same
		439	priority that were put into the ready queue earlier have been resumed.
		440
		441	=item $coro->suspend
		442
		443	Suspends the specified coro. A suspended coro works just like any other
		444	coro, except that the scheduler will not select a suspended coro for
		445	execution.
		446
		447	Suspending a coro can be useful when you want to keep the coro from
		448	running, but you don't want to destroy it, or when you want to temporarily
		449	freeze a coro (e.g. for debugging) to resume it later.
		450
		451	A scenario for the former would be to suspend all (other) coros after a
		452	fork and keep them alive, so their destructors aren't called, but new
		453	coros can be created.
		454
		455	=item $coro->resume
		456
		457	If the specified coro was suspended, it will be resumed. Note that when
		458	the coro was in the ready queue when it was suspended, it might have been
		459	unreadied by the scheduler, so an activation might have been lost.
		460
		461	To avoid this, it is best to put a suspended coro into the ready queue
		462	unconditionally, as every synchronisation mechanism must protect itself
		463	against spurious wakeups, and the one in the Coro family certainly do
		464	that.
		465
		466	=item $is_ready = $coro->is_ready
		467
		468	Returns true iff the Coro object is in the ready queue. Unless the Coro
		469	object gets destroyed, it will eventually be scheduled by the scheduler.
		470
		471	=item $is_running = $coro->is_running
		472
		473	Returns true iff the Coro object is currently running. Only one Coro object
		474	can ever be in the running state (but it currently is possible to have
		475	multiple running Coro::States).
		476
		477	=item $is_suspended = $coro->is_suspended
		478
		479	Returns true iff this Coro object has been suspended. Suspended Coros will
		480	not ever be scheduled.
		481
		482	=item $coro->cancel (arg...)
		483
		484	Terminates the given Coro and makes it return the given arguments as
		485	status (default: the empty list). Never returns if the Coro is the
		486	current Coro.
		487
		488	=cut
		489
		490	sub cancel {
		491	my $self = shift;
		492
		493	if ($current == $self) {
		494	terminate @_;
		495	} else {
		496	$self->{_status} = [@_];
		497	Coro::State::cancel $self;
271	{	498	}
272	# remember current coroutine	499	}
		500
		501	=item $coro->schedule_to
		502
		503	Puts the current coro to sleep (like C<Coro::schedule>), but instead
		504	of continuing with the next coro from the ready queue, always switch to
		505	the given coro object (regardless of priority etc.). The readyness
		506	state of that coro isn't changed.
		507
		508	This is an advanced method for special cases - I'd love to hear about any
		509	uses for this one.
		510
		511	=item $coro->cede_to
		512
		513	Like C<schedule_to>, but puts the current coro into the ready
		514	queue. This has the effect of temporarily switching to the given
		515	coro, and continuing some time later.
		516
		517	This is an advanced method for special cases - I'd love to hear about any
		518	uses for this one.
		519
		520	=item $coro->throw ([$scalar])
		521
		522	If C<$throw> is specified and defined, it will be thrown as an exception
		523	inside the coro at the next convenient point in time. Otherwise
		524	clears the exception object.
		525
		526	Coro will check for the exception each time a schedule-like-function
		527	returns, i.e. after each C<schedule>, C<cede>, C<< Coro::Semaphore->down
		528	>>, C<< Coro::Handle->readable >> and so on. Most of these functions
		529	detect this case and return early in case an exception is pending.
		530
		531	The exception object will be thrown "as is" with the specified scalar in
		532	C<$@>, i.e. if it is a string, no line number or newline will be appended
		533	(unlike with C<die>).
		534
		535	This can be used as a softer means than C<cancel> to ask a coro to
		536	end itself, although there is no guarantee that the exception will lead to
		537	termination, and if the exception isn't caught it might well end the whole
		538	program.
		539
		540	You might also think of C<throw> as being the moral equivalent of
		541	C<kill>ing a coro with a signal (in this case, a scalar).
		542
		543	=item $coro->join
		544
		545	Wait until the coro terminates and return any values given to the
		546	C<terminate> or C<cancel> functions. C<join> can be called concurrently
		547	from multiple coro, and all will be resumed and given the status
		548	return once the C<$coro> terminates.
		549
		550	=cut
		551
		552	sub join {
		553	my $self = shift;
		554
		555	unless ($self->{_status}) {
273	my $current = $Coro::current;	556	my $current = $current;
274		557
275	# register a hypothetical event handler	558	push @{$self->{_on_destroy}}, sub {
276	on_event_invoke sub {
277	# wake up sleeping coroutine
278	$current->ready;	559	$current->ready;
279	undef $current;	560	undef $current;
280	};	561	};
281		562
282	# call schedule until event occured.
283	# in case we are woken up for other reasons
284	# (current still defined), loop.
285	Coro::schedule while $current;
286	}
287
288	=item cede
289
290	"Cede" to other coroutines. This function puts the current coroutine into the
291	ready queue and calls C<schedule>, which has the effect of giving up the
292	current "timeslice" to other coroutines of the same or higher priority.
293
294	Returns true if at least one coroutine switch has happened.
295
296	=item Coro::cede_notself
297
298	Works like cede, but is not exported by default and will cede to any
299	coroutine, regardless of priority, once.
300
301	Returns true if at least one coroutine switch has happened.
302
303	=item terminate [arg...]
304
305	Terminates the current coroutine with the given status values (see L<cancel>).
306
307	=cut
308
309	sub terminate {
310	$current->cancel (@_);
311	}
312
313	=back
314
315	# dynamic methods
316
317	=head2 COROUTINE METHODS
318
319	These are the methods you can call on coroutine objects.
320
321	=over 4
322
323	=item new Coro \&sub [, @args...]
324
325	Create a new coroutine and return it. When the sub returns the coroutine
326	automatically terminates as if C<terminate> with the returned values were
327	called. To make the coroutine run you must first put it into the ready queue
328	by calling the ready method.
329
330	Calling C<exit> in a coroutine will not work correctly, so do not do that.
331
332	=cut
333
334	sub _run_coro {
335	terminate &{+shift};
336	}
337
338	sub new {
339	my $class = shift;
340
341	$class->SUPER::new (\&_run_coro, @_)
342	}
343
344	=item $success = $coroutine->ready
345
346	Put the given coroutine into the ready queue (according to it's priority)
347	and return true. If the coroutine is already in the ready queue, do nothing
348	and return false.
349
350	=item $is_ready = $coroutine->is_ready
351
352	Return wether the coroutine is currently the ready queue or not,
353
354	=item $coroutine->cancel (arg...)
355
356	Terminates the given coroutine and makes it return the given arguments as
357	status (default: the empty list). Never returns if the coroutine is the
358	current coroutine.
359
360	=cut
361
362	sub cancel {
363	my $self = shift;
364	$self->{status} = [@_];
365
366	if ($current == $self) {
367	push @destroy, $self;
368	$manager->ready;
369	&schedule while 1;
370	} else {
371	$self->_cancel;
372	}
373	}
374
375	=item $coroutine->join
376
377	Wait until the coroutine terminates and return any values given to the
378	C<terminate> or C<cancel> functions. C<join> can be called multiple times
379	from multiple coroutine.
380
381	=cut
382
383	sub join {
384	my $self = shift;
385
386	unless ($self->{status}) {
387	my $current = $current;
388
389	push @{$self->{destroy_cb}}, sub {
390	$current->ready;
391	undef $current;
392	};
393
394	&schedule while $current;	563	&schedule while $current;
395	}	564	}
396		565
397	wantarray ? @{$self->{status}} : $self->{status}[0];	566	wantarray ? @{$self->{_status}} : $self->{_status}[0];
398	}	567	}
399		568
400	=item $coroutine->on_destroy (\&cb)	569	=item $coro->on_destroy (\&cb)
401		570
402	Registers a callback that is called when this coroutine gets destroyed,	571	Registers a callback that is called when this coro gets destroyed,
403	but before it is joined. The callback gets passed the terminate arguments,	572	but before it is joined. The callback gets passed the terminate arguments,
404	if any.	573	if any, and I<must not> die, under any circumstances.
405		574
406	=cut	575	=cut
407		576
408	sub on_destroy {	577	sub on_destroy {
409	my ($self, $cb) = @_;	578	my ($self, $cb) = @_;
410		579
411	push @{ $self->{destroy_cb} }, $cb;	580	push @{ $self->{_on_destroy} }, $cb;
412	}	581	}
413		582
414	=item $oldprio = $coroutine->prio ($newprio)	583	=item $oldprio = $coro->prio ($newprio)
415		584
416	Sets (or gets, if the argument is missing) the priority of the	585	Sets (or gets, if the argument is missing) the priority of the
417	coroutine. Higher priority coroutines get run before lower priority	586	coro. Higher priority coro get run before lower priority
418	coroutines. Priorities are small signed integers (currently -4 .. +3),	587	coro. Priorities are small signed integers (currently -4 .. +3),
419	that you can refer to using PRIO_xxx constants (use the import tag :prio	588	that you can refer to using PRIO_xxx constants (use the import tag :prio
420	to get then):	589	to get then):
421		590
422	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	591	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
423	3 > 1 > 0 > -1 > -3 > -4	592	3 > 1 > 0 > -1 > -3 > -4
424		593
425	# set priority to HIGH	594	# set priority to HIGH
426	current->prio(PRIO_HIGH);	595	current->prio (PRIO_HIGH);
427		596
428	The idle coroutine ($Coro::idle) always has a lower priority than any	597	The idle coro ($Coro::idle) always has a lower priority than any
429	existing coroutine.	598	existing coro.
430		599
431	Changing the priority of the current coroutine will take effect immediately,	600	Changing the priority of the current coro will take effect immediately,
432	but changing the priority of coroutines in the ready queue (but not	601	but changing the priority of coro in the ready queue (but not
433	running) will only take effect after the next schedule (of that	602	running) will only take effect after the next schedule (of that
434	coroutine). This is a bug that will be fixed in some future version.	603	coro). This is a bug that will be fixed in some future version.
435		604
436	=item $newprio = $coroutine->nice ($change)	605	=item $newprio = $coro->nice ($change)
437		606
438	Similar to C<prio>, but subtract the given value from the priority (i.e.	607	Similar to C<prio>, but subtract the given value from the priority (i.e.
439	higher values mean lower priority, just as in unix).	608	higher values mean lower priority, just as in unix).
440		609
441	=item $olddesc = $coroutine->desc ($newdesc)	610	=item $olddesc = $coro->desc ($newdesc)
442		611
443	Sets (or gets in case the argument is missing) the description for this	612	Sets (or gets in case the argument is missing) the description for this
444	coroutine. This is just a free-form string you can associate with a coroutine.	613	coro. This is just a free-form string you can associate with a
		614	coro.
		615
		616	This method simply sets the C<< $coro->{desc} >> member to the given
		617	string. You can modify this member directly if you wish.
445		618
446	=cut	619	=cut
447		620
448	sub desc {	621	sub desc {
449	my $old = $_[0]{desc};	622	my $old = $_[0]{desc};
450	$_[0]{desc} = $_[1] if @_ > 1;	623	$_[0]{desc} = $_[1] if @_ > 1;
451	$old;	624	$old;
452	}	625	}
453		626
		627	sub transfer {
		628	require Carp;
		629	Carp::croak ("You must not call ->transfer on Coro objects. Use Coro::State objects or the ->schedule_to method. Caught");
		630	}
		631
454	=back	632	=back
455		633
456	=head2 GLOBAL FUNCTIONS	634	=head1 GLOBAL FUNCTIONS
457		635
458	=over 4	636	=over 4
459		637
460	=item Coro::nready	638	=item Coro::nready
461		639
462	Returns the number of coroutines that are currently in the ready state,	640	Returns the number of coro that are currently in the ready state,
463	i.e. that can be swicthed to. The value C<0> means that the only runnable	641	i.e. that can be switched to by calling C<schedule> directory or
		642	indirectly. The value C<0> means that the only runnable coro is the
464	coroutine is the currently running one, so C<cede> would have no effect,	643	currently running one, so C<cede> would have no effect, and C<schedule>
465	and C<schedule> would cause a deadlock unless there is an idle handler	644	would cause a deadlock unless there is an idle handler that wakes up some
466	that wakes up some coroutines.	645	coro.
467		646
468	=item my $guard = Coro::guard { ... }	647	=item my $guard = Coro::guard { ... }
469		648
470	This creates and returns a guard object. Nothing happens until the objetc	649	This function still exists, but is deprecated. Please use the
471	gets destroyed, in which case the codeblock given as argument will be	650	C<Guard::guard> function instead.
472	executed. This is useful to free locks or other resources in case of a
473	runtime error or when the coroutine gets canceled, as in both cases the
474	guard block will be executed. The guard object supports only one method,
475	C<< ->cancel >>, which will keep the codeblock from being executed.
476		651
477	Example: set some flag and clear it again when the coroutine gets canceled
478	or the function returns:
479
480	sub do_something {
481	my $guard = Coro::guard { $busy = 0 };
482	$busy = 1;
483
484	# do something that requires $busy to be true
485	}
486
487	=cut	652	=cut
488		653
489	sub guard(&) {	654	BEGIN { *guard = \&Guard::guard }
490	bless \(my $cb = $_[0]), "Coro::guard"
491	}
492
493	sub Coro::guard::cancel {
494	${$_[0]} = sub { };
495	}
496
497	sub Coro::guard::DESTROY {
498	${$_[0]}->();
499	}
500
501		655
502	=item unblock_sub { ... }	656	=item unblock_sub { ... }
503		657
504	This utility function takes a BLOCK or code reference and "unblocks" it,	658	This utility function takes a BLOCK or code reference and "unblocks" it,
505	returning the new coderef. This means that the new coderef will return	659	returning a new coderef. Unblocking means that calling the new coderef
506	immediately without blocking, returning nothing, while the original code	660	will return immediately without blocking, returning nothing, while the
507	ref will be called (with parameters) from within its own coroutine.	661	original code ref will be called (with parameters) from within another
		662	coro.
508		663
509	The reason this fucntion exists is that many event libraries (such as the	664	The reason this function exists is that many event libraries (such as the
510	venerable L<Event\|Event> module) are not coroutine-safe (a weaker form	665	venerable L<Event\|Event> module) are not thread-safe (a weaker form
511	of thread-safety). This means you must not block within event callbacks,	666	of reentrancy). This means you must not block within event callbacks,
512	otherwise you might suffer from crashes or worse.	667	otherwise you might suffer from crashes or worse. The only event library
		668	currently known that is safe to use without C<unblock_sub> is L<EV>.
513		669
514	This function allows your callbacks to block by executing them in another	670	This function allows your callbacks to block by executing them in another
515	coroutine where it is safe to block. One example where blocking is handy	671	coro where it is safe to block. One example where blocking is handy
516	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to	672	is when you use the L<Coro::AIO\|Coro::AIO> functions to save results to
517	disk.	673	disk, for example.
518		674
519	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when	675	In short: simply use C<unblock_sub { ... }> instead of C<sub { ... }> when
520	creating event callbacks that want to block.	676	creating event callbacks that want to block.
		677
		678	If your handler does not plan to block (e.g. simply sends a message to
		679	another coro, or puts some other coro into the ready queue), there is
		680	no reason to use C<unblock_sub>.
		681
		682	Note that you also need to use C<unblock_sub> for any other callbacks that
		683	are indirectly executed by any C-based event loop. For example, when you
		684	use a module that uses L<AnyEvent> (and you use L<Coro::AnyEvent>) and it
		685	provides callbacks that are the result of some event callback, then you
		686	must not block either, or use C<unblock_sub>.
521		687
522	=cut	688	=cut
523		689
524	our @unblock_queue;	690	our @unblock_queue;
525		691
526	# we create a special coro because we want to cede,	692	# we create a special coro because we want to cede,
527	# to reduce pressure on the coro pool (because most callbacks	693	# to reduce pressure on the coro pool (because most callbacks
528	# return immediately and can be reused) and because we cannot cede	694	# return immediately and can be reused) and because we cannot cede
529	# inside an event callback.	695	# inside an event callback.
530	our $unblock_scheduler = async {	696	our $unblock_scheduler = new Coro sub {
531	while () {	697	while () {
532	while (my $cb = pop @unblock_queue) {	698	while (my $cb = pop @unblock_queue) {
533	# this is an inlined copy of async_pool	699	&async_pool (@$cb);
534	my $coro = (pop @pool or new Coro \&pool_handler);
535		700
536	$coro->{_invoke} = $cb;
537	$coro->ready;
538	cede; # for short-lived callbacks, this reduces pressure on the coro pool	701	# for short-lived callbacks, this reduces pressure on the coro pool
		702	# as the chance is very high that the async_poll coro will be back
		703	# in the idle state when cede returns
		704	cede;
539	}	705	}
540	schedule; # sleep well	706	schedule; # sleep well
541	}	707	}
542	};	708	};
		709	$unblock_scheduler->{desc} = "[unblock_sub scheduler]";
543		710
544	sub unblock_sub(&) {	711	sub unblock_sub(&) {
545	my $cb = shift;	712	my $cb = shift;
546		713
547	sub {	714	sub {
548	unshift @unblock_queue, [$cb, @_];	715	unshift @unblock_queue, [$cb, @_];
549	$unblock_scheduler->ready;	716	$unblock_scheduler->ready;
550	}	717	}
551	}	718	}
552		719
		720	=item $cb = Coro::rouse_cb
		721
		722	Create and return a "rouse callback". That's a code reference that,
		723	when called, will remember a copy of its arguments and notify the owner
		724	coro of the callback.
		725
		726	See the next function.
		727
		728	=item @args = Coro::rouse_wait [$cb]
		729
		730	Wait for the specified rouse callback (or the last one that was created in
		731	this coro).
		732
		733	As soon as the callback is invoked (or when the callback was invoked
		734	before C<rouse_wait>), it will return the arguments originally passed to
		735	the rouse callback. In scalar context, that means you get the I<last>
		736	argument, just as if C<rouse_wait> had a C<return ($a1, $a2, $a3...)>
		737	statement at the end.
		738
		739	See the section B<HOW TO WAIT FOR A CALLBACK> for an actual usage example.
		740
553	=back	741	=back
554		742
555	=cut	743	=cut
556		744
557	1;	745	1;
558		746
		747	=head1 HOW TO WAIT FOR A CALLBACK
		748
		749	It is very common for a coro to wait for some callback to be
		750	called. This occurs naturally when you use coro in an otherwise
		751	event-based program, or when you use event-based libraries.
		752
		753	These typically register a callback for some event, and call that callback
		754	when the event occured. In a coro, however, you typically want to
		755	just wait for the event, simplyifying things.
		756
		757	For example C<< AnyEvent->child >> registers a callback to be called when
		758	a specific child has exited:
		759
		760	my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
		761
		762	But from within a coro, you often just want to write this:
		763
		764	my $status = wait_for_child $pid;
		765
		766	Coro offers two functions specifically designed to make this easy,
		767	C<Coro::rouse_cb> and C<Coro::rouse_wait>.
		768
		769	The first function, C<rouse_cb>, generates and returns a callback that,
		770	when invoked, will save its arguments and notify the coro that
		771	created the callback.
		772
		773	The second function, C<rouse_wait>, waits for the callback to be called
		774	(by calling C<schedule> to go to sleep) and returns the arguments
		775	originally passed to the callback.
		776
		777	Using these functions, it becomes easy to write the C<wait_for_child>
		778	function mentioned above:
		779
		780	sub wait_for_child($) {
		781	my ($pid) = @_;
		782
		783	my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
		784
		785	my ($rpid, $rstatus) = Coro::rouse_wait;
		786	$rstatus
		787	}
		788
		789	In the case where C<rouse_cb> and C<rouse_wait> are not flexible enough,
		790	you can roll your own, using C<schedule>:
		791
		792	sub wait_for_child($) {
		793	my ($pid) = @_;
		794
		795	# store the current coro in $current,
		796	# and provide result variables for the closure passed to ->child
		797	my $current = $Coro::current;
		798	my ($done, $rstatus);
		799
		800	# pass a closure to ->child
		801	my $watcher = AnyEvent->child (pid => $pid, cb => sub {
		802	$rstatus = $_[1]; # remember rstatus
		803	$done = 1; # mark $rstatus as valud
		804	});
		805
		806	# wait until the closure has been called
		807	schedule while !$done;
		808
		809	$rstatus
		810	}
		811
		812
559	=head1 BUGS/LIMITATIONS	813	=head1 BUGS/LIMITATIONS
560		814
561	- you must make very sure that no coro is still active on global	815	=over 4
562	destruction. very bad things might happen otherwise (usually segfaults).
563		816
		817	=item fork with pthread backend
		818
		819	When Coro is compiled using the pthread backend (which isn't recommended
		820	but required on many BSDs as their libcs are completely broken), then
		821	coro will not survive a fork. There is no known workaround except to
		822	fix your libc and use a saner backend.
		823
		824	=item perl process emulation ("threads")
		825
564	- this module is not thread-safe. You should only ever use this module	826	This module is not perl-pseudo-thread-safe. You should only ever use this
565	from the same thread (this requirement might be losened in the future	827	module from the first thread (this requirement might be removed in the
566	to allow per-thread schedulers, but Coro::State does not yet allow	828	future to allow per-thread schedulers, but Coro::State does not yet allow
567	this).	829	this). I recommend disabling thread support and using processes, as having
		830	the windows process emulation enabled under unix roughly halves perl
		831	performance, even when not used.
		832
		833	=item coro switching is not signal safe
		834
		835	You must not switch to another coro from within a signal handler
		836	(only relevant with %SIG - most event libraries provide safe signals).
		837
		838	That means you I<MUST NOT> call any function that might "block" the
		839	current coro - C<cede>, C<schedule> C<< Coro::Semaphore->down >> or
		840	anything that calls those. Everything else, including calling C<ready>,
		841	works.
		842
		843	=back
		844
		845
		846	=head1 WINDOWS PROCESS EMULATION
		847
		848	A great many people seem to be confused about ithreads (for example, Chip
		849	Salzenberg called me unintelligent, incapable, stupid and gullible,
		850	while in the same mail making rather confused statements about perl
		851	ithreads (for example, that memory or files would be shared), showing his
		852	lack of understanding of this area - if it is hard to understand for Chip,
		853	it is probably not obvious to everybody).
		854
		855	What follows is an ultra-condensed version of my talk about threads in
		856	scripting languages given onthe perl workshop 2009:
		857
		858	The so-called "ithreads" were originally implemented for two reasons:
		859	first, to (badly) emulate unix processes on native win32 perls, and
		860	secondly, to replace the older, real thread model ("5.005-threads").
		861
		862	It does that by using threads instead of OS processes. The difference
		863	between processes and threads is that threads share memory (and other
		864	state, such as files) between threads within a single process, while
		865	processes do not share anything (at least not semantically). That
		866	means that modifications done by one thread are seen by others, while
		867	modifications by one process are not seen by other processes.
		868
		869	The "ithreads" work exactly like that: when creating a new ithreads
		870	process, all state is copied (memory is copied physically, files and code
		871	is copied logically). Afterwards, it isolates all modifications. On UNIX,
		872	the same behaviour can be achieved by using operating system processes,
		873	except that UNIX typically uses hardware built into the system to do this
		874	efficiently, while the windows process emulation emulates this hardware in
		875	software (rather efficiently, but of course it is still much slower than
		876	dedicated hardware).
		877
		878	As mentioned before, loading code, modifying code, modifying data
		879	structures and so on is only visible in the ithreads process doing the
		880	modification, not in other ithread processes within the same OS process.
		881
		882	This is why "ithreads" do not implement threads for perl at all, only
		883	processes. What makes it so bad is that on non-windows platforms, you can
		884	actually take advantage of custom hardware for this purpose (as evidenced
		885	by the forks module, which gives you the (i-) threads API, just much
		886	faster).
		887
		888	Sharing data is in the i-threads model is done by transfering data
		889	structures between threads using copying semantics, which is very slow -
		890	shared data simply does not exist. Benchmarks using i-threads which are
		891	communication-intensive show extremely bad behaviour with i-threads (in
		892	fact, so bad that Coro, which cannot take direct advantage of multiple
		893	CPUs, is often orders of magnitude faster because it shares data using
		894	real threads, refer to my talk for details).
		895
		896	As summary, i-threads use threads to implement processes, while
		897	the compatible forks module uses processes to emulate, uhm,
		898	processes. I-threads slow down every perl program when enabled, and
		899	outside of windows, serve no (or little) practical purpose, but
		900	disadvantages every single-threaded Perl program.
		901
		902	This is the reason that I try to avoid the name "ithreads", as it is
		903	misleading as it implies that it implements some kind of thread model for
		904	perl, and prefer the name "windows process emulation", which describes the
		905	actual use and behaviour of it much better.
568		906
569	=head1 SEE ALSO	907	=head1 SEE ALSO
570		908
		909	Event-Loop integration: L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		910
		911	Debugging: L<Coro::Debug>.
		912
571	Support/Utility: L<Coro::Cont>, L<Coro::Specific>, L<Coro::State>, L<Coro::Util>.	913	Support/Utility: L<Coro::Specific>, L<Coro::Util>.
572		914
573	Locking/IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>, L<Coro::SemaphoreSet>, L<Coro::RWLock>.	915	Locking and IPC: L<Coro::Signal>, L<Coro::Channel>, L<Coro::Semaphore>,
		916	L<Coro::SemaphoreSet>, L<Coro::RWLock>.
574		917
575	Event/IO: L<Coro::Timer>, L<Coro::Event>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::Select>.	918	I/O and Timers: L<Coro::Timer>, L<Coro::Handle>, L<Coro::Socket>, L<Coro::AIO>.
576		919
577	Embedding: L<Coro:MakeMaker>	920	Compatibility with other modules: L<Coro::LWP> (but see also L<AnyEvent::HTTP> for
		921	a better-working alternative), L<Coro::BDB>, L<Coro::Storable>,
		922	L<Coro::Select>.
		923
		924	XS API: L<Coro::MakeMaker>.
		925
		926	Low level Configuration, Thread Environment, Continuations: L<Coro::State>.
578		927
579	=head1 AUTHOR	928	=head1 AUTHOR
580		929
581	Marc Lehmann <schmorp@schmorp.de>	930	Marc Lehmann <schmorp@schmorp.de>
582	http://home.schmorp.de/	931	http://home.schmorp.de/

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Revision 1.114 by root, Wed Jan 24 16:22:08 2007 UTC vs.
Revision 1.270 by root, Thu Oct 1 23:50:23 2009 UTC